1. Field of the Invention
The present invention relates to a ferrite phase shifter which generates a magnetic field by passing a current through a coil from outside of a rectangular waveguide to change magnetic characteristics of a ferrite and to change a waveguide wavelength of a high frequency wave propagating in the waveguide, thereby changing the phase of the high frequency wave. The invention also relates to an automatic matching apparatus having such a ferrite phase shifter.
2. Description of the Related Art
Ferrite phase shifters are known, in which a ferrite is disposed in a waveguide to generate a magnetic field for changing the phase of a high frequency wave propagating in the waveguide. For example, such a ferrite phase shifter is configured as shown in FIGS. 18 to 20. A ferrite phase shifter 100 shown in FIGS. 18 to 20 includes a substantially square cylindrical rectangular waveguide 101 formed by a top face 101a, a bottom face 101b and two side faces 101c, and blade-like flanges 101d to serve as coupling sections for coupling with other rectangular waveguides are formed on both longitudinal ends of the waveguide. A coil 102 is substantially helically wound around the rectangular waveguide 101 substantially in the middle thereof. A sheet-like spacer 103 made of a dielectric material is provided at each of upper and lower positions in the rectangular waveguide 101, and the spacers 103 are disposed to extend in the longitudinal direction of the rectangular waveguide 101. The upper and lower spacers 103 are secured so as to sandwich a rectangular parallelepiped ferrite 104 between them.
The ferrite phase shifter is used as follows. For example, the rectangular waveguide 101 is coupled with other rectangular waveguides to form a waveguide path, and a high frequency wave is propagated in the rectangular waveguide 101 through the waveguide path. A current is passed through the coil 102 from the outside of the rectangular waveguide 101 to generate a magnetic field. Thus, magnetic characteristics of the ferrite are changed to change a waveguide wavelength of the high frequency wave, whereby the phase of the propagating high frequency wave is changed (see Non-Patent Document 1).    Non-Patent Document 1: Tadashi Hashimoto, Microwave Ferrite and Applications, issued by Sogo Denshi Shuppan-sha on May 10, 1997, pp. 111-114